Process for producing carbon foams for energy storage devices

Abstract

A high energy density capacitor incorporating a variety of carbon foam electrodes is described. The foams, derived from the pyrolysis of resorcinol-formaldehyde and related polymers, are high density (0.1 g/cc-1.0 g/cc) electrically conductive and have high surface areas (400 m.sup.2 /g-1000 m.sup.2 /g). Capacitances on the order of several tens of farad per gram of electrode are achieved.

Claims

1. A process for producing high density carbon foam, selected from the group of aerogel carbon foam, xerogel carbon foam and xerogel-aerogel carbon foam, having a density of above 0.3 g/cc and up to about 1.2 g/cc, and having a surface area of over 300 m.sup.2 /g to about 1200 m.sup.2 /g, including the steps of:

forming a mixture from at least one mole of resorcinol or catechol and two moles of formaldehyde in the presence of a basic catalyst, and with a mole ratio of resorcinol or catechol to catalyst of 50-400;

forming an aquagel from the thus formed mixture; and

drying the thus formed aquagel.

2. The process of claim 1, additionally including the step of pyrolyzing the thus dried aquagel at a temperature in the range of 600.degree.-2100.degree. C. in an inert atmosphere, thereby forming the high density carbon foam.

3. The process of claim 1, wherein the step of drying is carried out by evaporation thereby forming an xerogel.

4. The process of claim 1, wherein the step of drying is carried out under supercritical drying conditions thereby forming an aerogel.

5. The process of claim 1, wherein the step of drying is carried out first by partial evaporation and then by partial supercritical drying, thereby forming a hybrid xerogel-aerogel.

6. The process of claim 1, wherein the step of drying is carried out first by partial supercritical drying and then by partial evaporation thereby forming a hybrid xerogel-aerogel.

7. The process of claim 1, wherein the step of forming the mixture includes adding a quantity of deionized and distilled water thereto.

8. The process of claim 7, wherein the catalyst is sodium carbonate.

9. The process of claim 8, wherein the step of forming the aquagel includes the step of curing the mixture under time periods and temperatures.

10. The process of claim 9, wherein the mixture is cured for 24 hours at room temperature, followed by 24 hours at 50.degree. C., and then 72 hours at 95.degree. C., thereby producing an aquagel.

11. The process of claim 10, wherein the step of drying includes the steps of placing the thus cured aquagel in an organic solvent selected from the group of acetone, methanol, isopropanol, and amyl acetate;

adding trifluoroacetic acid to the solvent to promote additional crosslinking; and

agitating to cause the solvent to diffuse into the aquagel thereby replacing water in the pores thereof.

12. The process of claim 11, additionally including the steps of placing the solvent filled gel in a container of the solvent such that the gel is submerged therein;

placing the container in a jacketed pressure vessel;

slowly bleeding air from the vessel while filling the vessel with liquefied carbon dioxide at a pressure;

maintaining the vessel at a temperature, and retaining the gel in the liquefied carbon dioxide for a time period;

flushing the vessel with fresh carbon dioxide for a time period;

draining and refilling the vessel with liquefied carbon dioxide while retaining the gel covered thereby, until the solvent in the gel pores is replaced with carbon dioxide;

draining the carbon dioxide from the vessel to a level just above the gel;

heating the vessel to a temperature of about 50.degree. C. and at a pressure of about 1800 psi, and maintaining the temperature and pressure for a time period;

slowly reducing the pressure in the vessel while maintaining the temperature; and

removing from the vessel the thus formed organic aerogel having continuous porosity, pore sizes of less than 100 nm, surface area of 400-1000 m.sup.2 /g, and solid matrix of interconnected polymeric chains with characteristic diameters of 10 nm.

13. The process of claim 12, additionally including the step of pyrolyzing the thus formed organic aerogel at a temperature of 600.degree.-2100.degree. C. in an inert atmosphere selected from the group of nitrogen, argon, neon, and helium, thereby forming the carbon aerogel.

14. The process of claim 13, wherein the step of pyrolyzing is carried out at about 1050.degree. C. in a nitrogen atmosphere.